System and method for enhancing visual inspection of an object

ABSTRACT

A method for inspecting an object to assist in determining whether the object has a surface defect. The method includes moving the object in a first direction and illuminating the object under ambient lighting conditions. The method also includes capturing at least one image of the object under the ambient lighting conditions while the object moves in the first direction. In addition, the object is illuminated under object lighting conditions and at least one image of the object under the object lighting conditions is captured while the object moves in the first direction to provide at least one object image. Further, the method includes selecting at least one object image having at least one indication of a possible defect to provide images having defect candidates and comparing the defect candidates with previously defined characteristics associated with the defect to facilitate determination of whether a defect exists.

FIELD OF THE INVENTION

This invention relates to inspection systems, and more particularly, toa method for inspecting an object to assist in determining whether theobject has a surface defect by comparing defect candidates in imagescaptured under varied lighting conditions with previously definedcharacteristics associated with the defect to facilitate determinationof whether a defect exists.

BACKGROUND OF THE INVENTION

Inspection methods such as liquid penetrant, magnetic particle and eddycurrent inspection methods are frequently used to detect small flaws ordefects (i.e. less than approximately 2 mm size) on the surface of acomponent. Many surface inspection methods utilize chemicals orcomplicated equipment in order to achieve a high probability ofdetection of such defects. However, such inspection methods areenvironmentally unfriendly and expensive. Further, such inspectionmethods are time consuming and require a substantial amount of operatortraining in order to effectively operate the inspection equipment. It isdesirable to provide improved surface inspection techniques thatovercome the drawbacks of current methods.

SUMMARY OF INVENTION

A method for inspecting an object to assist in determining whether theobject has a surface defect is disclosed. The method includes moving theobject in a first direction and illuminating the object under ambientlighting conditions. The method also includes capturing at least oneimage of the object under the ambient lighting conditions while theobject moves in the first direction. In addition, the object isilluminated under object lighting conditions and at least one image ofthe object under the object lighting conditions is captured while theobject moves in the first direction to provide at least one objectimage. Further, the method includes selecting at least one object imagehaving at least one indication of a possible defect to provide imageshaving defect candidates. The defect candidates in the images are thencompared with previously defined characteristics associated with thedefect to facilitate determination of whether a defect exists.

Those skilled in the art may apply the respective features of thepresent invention jointly or severally in any combination orsub-combination.

BRIEF DESCRIPTION OF DRAWINGS

The teachings of the present disclosure can be readily understood byconsidering the following detailed description in conjunction with theaccompanying drawings, in which:

FIG. 1 is a side view system for performing automated visual inspectionof a surface of an object.

FIG. 2 is a top view of the system shown in FIG. 1.

FIGS. 3A and 3B depict an overall motion platform for the system.

FIGS. 4A-4B depict a method for detecting surface defects in accordancewith an aspect of the current invention.

FIG. 5 depicts a software and input/output (I/O) architecture inaccordance with the present invention.

FIG. 6 depicts software architecture for providing a parallel processingmechanism for a scanning process in accordance with the currentinvention.

FIG. 7 depicts a sample inspection report.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures.

DETAILED DESCRIPTION

Although various embodiments that incorporate the teachings of thepresent disclosure have been shown and described in detail herein, thoseskilled in the art can readily devise many other varied embodiments thatstill incorporate these teachings. The scope of the disclosure is notlimited in its application to the exemplary embodiment details ofconstruction and the arrangement of components set forth in thedescription or illustrated in the drawings. The disclosure encompassesother embodiments and of being practiced or of being carried out invarious ways. Also, it is to be understood that the phraseology andterminology used herein is for the purpose of description and should notbe regarded as limiting. The use of “including,” “comprising,” or“having” and variations thereof herein is meant to encompass the itemslisted thereafter and equivalents thereof as well as additional items.Unless specified or limited otherwise, the terms “mounted,” “connected,”“supported,” and “coupled” and variations thereof are used broadly andencompass direct and indirect mountings, connections, supports, andcouplings. Further, “connected” and “coupled” are not restricted tophysical or mechanical connections or couplings.

The current invention may be used to inspect objects such as generatorwedges used in electrical generators utilized in power generationequipment. It is desirable to enhance the ability to detect surfacedefects or flaws in a generator wedge, such as cracks or otherimperfections, in order to enhance performance and service life of thegenerator wedge. It is understood that the current invention is notlimited to inspecting generator wedges and may be used to inspect othertypes of components or objects to, for example, verify whether an objectmeets desired quality parameters and/or to measure process variability,provide process control and perform other tasks.

Referring to FIGS. 1 and 2, side and top views, respectively, are shownof a system 10 for performing automated visual inspection of a surface15 of an object 12. The system 10 includes an optical sensor 14 locatedinside a sensor hood 16. The optical sensor 14 includes an imagingdevice 18, such as a camera, and a lens 20. The system 10 also includesa linear stage 22 having a platform 24 that supports the object 12. Thelinear stage 22 is moved along a longitudinal X-axis by a motor 17controlled by a motion controller 21. Information regarding a positionof the linear stage 22 along the X-axis is provided to the motioncontroller 21 by an encoder 19.

The lens 20 and object 12 are spaced apart to provide a suitable fieldof view 26 for imaging the object 12. The hood 16 includes taperedsurfaces 28 that taper away from each other and extend toward the object12. A bottom portion 30 of the hood 16 includes at least one objectillumination source 32 such as a light emitting diode (“LED”) strobelight. For purposes of illustration, four object illumination sources 32are shown in FIG. 2 although it is understood that additional or fewerobject illumination sources 32 may be used. Each object illuminationsource 32 is oriented at a relatively large zenith angle relative to avertical axis 34 of the object 12 suitable for providing dark fieldillumination of the object 12. In dark field illumination, for example,a first portion of a defect on the object 12 may form a bright regionwhereas a second portion of the defect is not illuminated thus forming adark or shadow region. The bright and shadow regions are in the field ofview 26 of the optical sensor 14. Further, light that impinges on a flatsurface (i.e. a surface that does not include a defect) is reflected outof the field of view 26 of the optical sensor 14.

In addition, the system 10 includes at least one ambient illuminationsource 36 located inside the hood 16. The ambient illumination source 36may be an LED strobe light having a ring shape (“LED ring light”). In anembodiment, the lens 20 extends through the ring light. Operation of theoptical sensor 14, the ambient illumination source 36 and objectillumination sources 32 is controlled by a trigger control module 54.The trigger control module 54 triggers the optical sensor 14, ambientillumination source 36 and object illumination sources 32 to captureimages of the object 12 under selected lighting conditions as the object12 is moved along the X-axis by the linear stage 22 to provide anautomated inspection system.

A relative position of the ambient illumination source 36 and objectillumination sources 32 is adjustable to provide a plurality of tiltangles suitable for illuminating the object 12. Further, a position ofthe optical sensor 14 may be adjustable. A position of each objectillumination source 32 and/or optical sensor 14 is fixed after suitableillumination parameters are obtained during an illumination calibrationprocedure. FIGS. 3A and 3B depict an overall motion platform 42 for thesystem 10. The motion platform 42 includes X, Y, Z axes in a Cartesiancoordinate system and pan 38 and tilt 40 angles in a sphericalcoordinate system used to adjust a pointing direction of the opticalsensor 14 relative to the object 12. In addition, the linear stage 22moves the object 12 along the X axis.

Referring to FIGS. 4A-4B, a method 44 for detecting surface defects willnow be described. At step 46, the optical sensor 14 is calibratedrelative to a surface 15, or working plane, of the object 12 beinginspected by capturing a spatial relation between the optical sensor 14and surface 15. At step 48, the ambient illumination source 36 is turnedon to capture a registration image of the surface 15 under ambientlighting conditions as the object 12 is moved along the X-axis by thelinear stage 22. The optical sensor 14 is then activated to captureimages of the object 12 under various dark field illumination conditionsas the object 12 is moved along the X-axis by the linear stage 22 atstep 50. For example, the object illumination sources 32 may be turnedon and off in a desired sequence, pattern, simultaneously, with variedlighting levels etc. as the object 12 is moved by the linear stage 22during image capture. At step 52, the images captured under ambient anddark field lighting conditions are registered based on position readingstaken from the linear stage 22 as the linear stage 22 moves along theX-axis. For purposes of registration, it is assumed that the object 12is undergoing pure translation movement during registration. Thus,accurate registration is obtained between images obtained underdifferent illumination configurations and their corresponding spatialpositions.

At step 60, the images are processed through a plurality of preliminarypruning stages that identify images which include an indication of apossible defect such as a crack. Images that do not have the indicationare then ruled out. For example, in a first pruning stage, the imagesare screened to identify images that include a characteristic indicativeof dark field illumination, such as a bright or shadow region, and thusthe existence of a possible defect. Remaining images that do not includea characteristic indicative of dark field illumination are ruled out sothat no further processing is undertaken for the ruled out images. In asecond pruning stage, the images identified in the first pruning stageare again screened to identify whether the images include an indicationof an additional or alternative characteristic indicative of a possibledefect. For example, each image in the second pruning stage may becompared to the registration image to determine whether any differencesbetween the registration image and an image being screened areindicative of a possible defect. It is understood that additionalpruning stages may be used. Alternatively, a single preliminary pruningstage may be used.

At the conclusion of the preliminary pruning stages, a plurality ofscreened images remains each including possible defect candidates. Atstep 62, the possible defects identified in the screened images are thencompared with previously defined characteristics associated with thedefect. In an embodiment, the characteristics may be based on previousobservations of the defect under varied lighting conditions that havebeen noted and compiled by the inventors herein. In the case of a defectsuch as a crack, the characteristics may include crack length, width,thickness, orientation and other characteristics under variousillumination conditions.

At step 64, a detailed analysis is then performed by trained personnelto determine the likelihood that a defect candidate is an actual defecton a surface of the object. The determination is based on a comparisonof a defect candidate with the predetermined crack characteristics,illumination configuration for the image, camera intrinsic and extrinsicparameters and other factors.

Referring to FIG. 5, software and input/output (I/O) architecture 70 inaccordance with the present invention is shown. The architecture 70enables simultaneous image acquisition and processing in order tosatisfy challenging time constraints. The architecture 70 includes aplurality of modules including a user interface module or graphical userinterface (“GUI”) 72 that enables user interaction and provides a resultdisplay. The architecture also includes a Configuration Module 74 forsetting parameters for software and hardware. This includes configuringan optical sensor such as a Camera 76 and a Frame Grabber 78 via aCamera Software Development Kit (“SDK”) 80 and a Frame Grabber SDK 82which include camera and frame grabber libraries, respectively, thatenable configuration and image acquisition. In addition, architecture 70includes a Control Module 84 for sending commands and instructions suchas initial, start, stop, emergency stop, linear stage position readingand others to a Controller 86 via a Controller SDK 88 that providesaccess to a controller library and serves as an interface. TheController 86 controls a Motion Controller 88 that controls movement ofthe linear stage 22 so that the object 12 is moved in a continuousmotion. The Controller 88 also controls a Triggering Control Module 90via a Digital I/O device 92. The Triggering Control Module 90 triggersthe object 32 and ambient 36 illumination sources and the camera 76 tocapture images of the object 12 under various lighting conditions aspreviously described. Further, the architecture 70 includes anAcquisition Module 94 that fetches images from the camera 76 and anAnalytics Module 96 for processing and analyzing images received from ajob queue 106 including batches of images to assist trained personnel indetermining whether the object 12 under inspection has defects. Datagenerated by the Analytics Module 96 may then be archived in a DataArchiving Module 98.

Referring to FIG. 6, software architecture 100 for providing a parallelprocessing mechanism for the scanning process is shown. The architecture100 includes a plurality of software threads. In particular, Thread A102 is used to control I/Os, e.g. sending commands and instructions tothe Motion Controller 88. Thread C 104 handles image acquisition andsends captured images to the job queue 106 for analytics processing. Theimages are preprocessed in Thread B 108 before the images are dividedinto small batches. The images are then sent to multiple analyticsthreads (B₁ . . . B_(n)) 110 for multi-stage pruning as previouslydescribed. Further, Thread B 108 collects decisions from the analyticsthreads and generates a consolidated decision regarding defects that isthen reviewed by trained personnel.

After each object 12 is scanned, a trained operator determines whether adefect exists on an object 12 and an inspection report is subsequentlygenerated. Referring to FIG. 7, a sample inspection report 112 is shown.The inspection report 112 includes information such as an identificationnumber 114 for each defect, corresponding batch number 116, date 118,time 120, surface inspected 122 and X and Y position 124 of the defecton the surface 15.

The system of the present invention may be configured as a portabledevice to enable remote inspection of objects. Further, the system doesnot utilize environmentally unfriendly materials used in conventionalmethods and requires very little technical training for an inspector. Ithas been found by the inventors herein that the system has a higher flawdetection capability, faster inspection speed and lower cost whencompared to current inspection methods. In addition, the system may beused for nondestructive evaluation (“NDE”) inspection of generatorwedges, machined parts and other components.

While particular embodiments of the present disclosure have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the disclosure. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this disclosure.

What is claimed is:
 1. A method for inspecting an object to assist indetermining whether the object has a surface defect, comprising: movingthe object in a first direction by a linear stage; illuminating theobject under ambient lighting conditions by at least one ambientillumination source; capturing at least one image of the object underthe ambient lighting conditions while the object moves in the firstdirection to provide a registration image by an optical sensor;illuminating the object under object lighting conditions by at least oneobject illumination source; capturing at least one image of the objectunder the object lighting conditions while the object moves in the firstdirection to provide at least one object image by the optical sensor;selecting at least one object image having at least one indication of apossible defect to provide images having defect candidates by acontroller; comparing the defect candidates with previously definedcharacteristics associated with the defect to facilitate determinationof whether a defect exists by the controller, the method furthercomprising registering the registration image captured under the ambientlighting conditions with the at least one image of the object capturedunder the object lighting conditions based on position readings from thelinear stage by the controller.
 2. The method according to claim 1,wherein an indication of a possible defect includes determining whetherthe at least one object image has a bright or a shadow region.
 3. Themethod according to claim 1, wherein an indication of a possible defectincludes comparing the object image with the registration image.
 4. Themethod according to claim 1, wherein a plurality of pruning stages areused to select the at least one object image.
 5. The method according toclaim 1, wherein the previously defined characteristics include length,width, thickness, orientation of a crack.
 6. The method according toclaim 1, wherein illuminating the object under object lightingconditions includes operating a plurality of object illumination sourcesin accordance with a desired sequence or operating the objectillumination sources simultaneously to provide the object lightingconditions.
 7. A method for inspecting an object to assist indetermining whether the object has a surface defect, comprising:providing a linear stage to move the object in a first direction;operating at least one ambient illumination source to illuminate theobject under ambient lighting conditions; providing an optical sensor tocapture at least one image of the object under the ambient lightingconditions while the object moves in the first direction to provide aregistration image; operating at least one object illumination source toilluminate the object under object lighting conditions; operating theoptical sensor to capture at least one image of the object under theobject lighting conditions while the object moves in the first directionto provide at least one object image; selecting at least one objectimage having at least one indication of a possible defect to provideimages having defect candidates by a controller; comparing the defectcandidates with previously defined characteristics associated with thedefect to facilitate determination of whether a defect exists by thecontroller, the method further comprising registering the registrationimage captured under the ambient lighting conditions with the at leastone image of the object captured under the object lighting conditionsbased on position readings from the linear stage by the controller. 8.The method according to claim 7, wherein an indication of a possibledefect includes determining whether the at least one object image has abright or a shadow region.
 9. The method according to claim 7, whereinan indication of a possible defect includes comparing the object imagewith the registration image.
 10. The method according to claim 7,wherein a plurality of pruning stages are used to select the at leastone object image.
 11. The method according to claim 7, wherein thepreviously defined characteristics include length, width, thickness,orientation of a crack.
 12. The method according to claim 7, whereinilluminating the object under object lighting conditions includesoperating a plurality of object illumination sources in accordance witha desired sequence or operating the object illumination sourcessimultaneously to provide the object lighting conditions.
 13. A systemfor inspecting an object to assist in determining whether the object hasa surface defect, comprising: a linear stage for moving the object in afirst direction; at least one ambient illumination source to illuminatethe object under ambient lighting conditions; an optical sensor tocapture at least one image of the object under the ambient lightingconditions; at least one object illumination source to illuminate theobject under object lighting conditions; and a controller forcontrolling the optical sensor and the ambient and objectionillumination sources, wherein the optical sensor captures at least oneimage of the object under the ambient lighting conditions to provide aregistration image and at least one image of the object under the objectlighting conditions while the object moves in the first direction,wherein the controller selects at least one object image having at leastone indication of a possible defect to provide images having defectcandidates, wherein the controller compares the defect candidates withpreviously defined characteristics associated with the defect tofacilitate determination of whether a defect exists, and wherein thecontroller registers the registration image captured under the ambientlighting conditions with the at least one image of the object capturedunder the object lighting conditions based on position readings from thelinear stage.
 14. The system according to claim 13, wherein the ambientand object illumination sources are light emitting diode (“LED”) strobelights.
 15. The system according to claim 14, wherein the ambientillumination source is an LED ring light.
 16. The system according toclaim 13, wherein an indication of a possible defect includesdetermining whether the at least one object image has a bright or ashadow region.
 17. The system according to claim 13, wherein anindication of a possible defect includes comparing the object image withthe registration image.
 18. The system according to claim 13, whereinthe previously defined characteristics include length, width, thickness,orientation of a crack.